Bottom Line:
N-Al volume fractions of 1 and 3% did not show enhancement in the average volumetric HoC, but higher volume fractions of 5, 7, and 10% increased the volumetric HoC by 5.82, 8.65, and 15.31%, respectively.N-Al2O3 and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the HoC in the tests.A combustion model that utilized Chemical Equilibrium with Applications was conducted as well and was shown to be in good agreement with the experimental results.

ABSTRACTAn experimental investigation of the combustion behavior of nano-aluminum (n-Al) and nano-aluminum oxide (n-Al2O3) particles stably suspended in biofuel (ethanol) as a secondary energy carrier was conducted. The heat of combustion (HoC) was studied using a modified static bomb calorimeter system. Combustion element composition and surface morphology were evaluated using a SEM/EDS system. N-Al and n-Al2O3 particles of 50- and 36-nm diameters, respectively, were utilized in this investigation. Combustion experiments were performed with volume fractions of 1, 3, 5, 7, and 10% for n-Al, and 0.5, 1, 3, and 5% for n-Al2O3. The results indicate that the amount of heat released from ethanol combustion increases almost linearly with n-Al concentration. N-Al volume fractions of 1 and 3% did not show enhancement in the average volumetric HoC, but higher volume fractions of 5, 7, and 10% increased the volumetric HoC by 5.82, 8.65, and 15.31%, respectively. N-Al2O3 and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the HoC in the tests. A combustion model that utilized Chemical Equilibrium with Applications was conducted as well and was shown to be in good agreement with the experimental results.

Figure 8: Adiabatic flame temperatures for ethanol and aluminum mixtures at stoichiometric conditions, for an initial temperature of 298 K.

Mentions:
The combustion kinetics was modeled using the NASA Chemical Equilibrium with Applications (CEA) computer program [31]. This code assumes a homogeneous system, calculates chemical equilibrium product concentrations, and determines thermodynamic properties for the product mixture. As shown in Figure 8, the calculated adiabatic flame temperatures for solid and vaporized aluminum in air were compared to liquid ethanol with Al and Al2O3 volumetric concentrations. It was assumed that all reactants were initially at room temperature (298 K). Ethanol with 10% Al concentration by volume resulted in a 6-9% increase in adiabatic flame temperature over the range of pressures' and an increase of 8.27% at the experimental 20 atm. The adiabatic flame temperature increase of 8.27% is comparable to the experimental HoC increase of 8.65% due to n-Al additives. On the other hand, ethanol with 5% Al2O3 volumetric concentration resulted in a 1-2% lower flame temperature than pure ethanol, agreeing with the experimental result that n-Al2O3 did not participate in the combustion.

Figure 8: Adiabatic flame temperatures for ethanol and aluminum mixtures at stoichiometric conditions, for an initial temperature of 298 K.

Mentions:
The combustion kinetics was modeled using the NASA Chemical Equilibrium with Applications (CEA) computer program [31]. This code assumes a homogeneous system, calculates chemical equilibrium product concentrations, and determines thermodynamic properties for the product mixture. As shown in Figure 8, the calculated adiabatic flame temperatures for solid and vaporized aluminum in air were compared to liquid ethanol with Al and Al2O3 volumetric concentrations. It was assumed that all reactants were initially at room temperature (298 K). Ethanol with 10% Al concentration by volume resulted in a 6-9% increase in adiabatic flame temperature over the range of pressures' and an increase of 8.27% at the experimental 20 atm. The adiabatic flame temperature increase of 8.27% is comparable to the experimental HoC increase of 8.65% due to n-Al additives. On the other hand, ethanol with 5% Al2O3 volumetric concentration resulted in a 1-2% lower flame temperature than pure ethanol, agreeing with the experimental result that n-Al2O3 did not participate in the combustion.

Bottom Line:
N-Al volume fractions of 1 and 3% did not show enhancement in the average volumetric HoC, but higher volume fractions of 5, 7, and 10% increased the volumetric HoC by 5.82, 8.65, and 15.31%, respectively.N-Al2O3 and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the HoC in the tests.A combustion model that utilized Chemical Equilibrium with Applications was conducted as well and was shown to be in good agreement with the experimental results.

ABSTRACTAn experimental investigation of the combustion behavior of nano-aluminum (n-Al) and nano-aluminum oxide (n-Al2O3) particles stably suspended in biofuel (ethanol) as a secondary energy carrier was conducted. The heat of combustion (HoC) was studied using a modified static bomb calorimeter system. Combustion element composition and surface morphology were evaluated using a SEM/EDS system. N-Al and n-Al2O3 particles of 50- and 36-nm diameters, respectively, were utilized in this investigation. Combustion experiments were performed with volume fractions of 1, 3, 5, 7, and 10% for n-Al, and 0.5, 1, 3, and 5% for n-Al2O3. The results indicate that the amount of heat released from ethanol combustion increases almost linearly with n-Al concentration. N-Al volume fractions of 1 and 3% did not show enhancement in the average volumetric HoC, but higher volume fractions of 5, 7, and 10% increased the volumetric HoC by 5.82, 8.65, and 15.31%, respectively. N-Al2O3 and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al2O3 to the HoC in the tests. A combustion model that utilized Chemical Equilibrium with Applications was conducted as well and was shown to be in good agreement with the experimental results.